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5.2.2 Electrode care
•
The pH-sensitive membrane glass must be handled with care and protected from
damage.
•
The inner reference solution of the glass electrode must cover the inner surface of
the membrane glass. Visually check the probes for trapped air bubbles. If air
bubbles are present, these can be removed by shaking downwards (like a
thermometer).
5.2.3 Cleaning the electrodes
If contamination on the glass membrane cannot be removed using a soft, damp cloth,
the following cleaning agents may be used.
General deposits: Non-scouring household cleaning agent
Limescale or metal hydroxide: Diluted hydrochloric acid (approx. 0.1%-3%) / 1-5
minutes
Oils and fats: Solvents such as alcohol and acetone
Biological coatings: Solution of diluted hydrochloric acid and pepsin. Leave to work
for a couple of hours; solvents (e.g. acetone) may not be used to clean electrodes with
plastic shafts since they can attack them.
Generally speaking, rinse sufficiently after each cleaning process.
If the ceramic diaphragm of the reference system that is installed on the side is blocked,
this can be cleaned in the same way as the glass membrane. You can also carefully
scrape it with a fingernail, razor blade or fine file. Make sure that the glass membrane
is not scratched.
5.2.4 Calibration
pH probe
Calibration is carried out as described in the operating instructions (the device section).
If the deviation is too great or fails, the electrode must be replaced.
Rx probe
The Rx probe is checked using the buffer solution Rx 475 mV. If the deviation of the
measured value is too large (40 mV), the electrode must be replaced. Caution: Rx
probes are end-calibrated at the factory.
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